Measuring and control method and apparatus



,July 20 1943. J. R. CAMPBELL 2,

MEASURING AND CONTROL METHOD AND APPARATUS Filed Feb. 8, 1939 Zhwehtor {JAMES R. CAMPBELL r e aa July 20, 194;; g

- MEASURING I v [New York 18f Claims.

This invention relates to a method and apparatus for measuring and/ or controllin'gthe contlon of an atmosphere. More particularly my ve'ntion relates to a method and apparatus for easuring and/or controlling the ratio between the rate of fuel flow and air flow to a furnace to maintain a desired furnace atmosphere therein,

r to maintain optimum combustion efficiency.

In the present state of the art industrial furacel atmospheres are divided; for convenience to four typical conditionsi (1) neutral; (2) xidizing; (3) reducing; ((4) special. Neutral tmospheres' are those in which there is praccally no free oxygen. oxidizing atmospheres ethos'e in which there is an appreciable amount 1'; free oxygen present. Reducing atmospheres re those in which there is, an element present M ving an unsatisfied afiinity for oxygen. pecial' atmospheres may be defined as those in hich there is introduced a gas or vapor for some particular purpose.

In industrial furnaces it is not only of importance to know the qualitative condition of the furnace atmosphere, butitis also of vital imrtance to know the quantitative condition. Thus certain operations require strongly oxidizatmospheres. Typical examples of such oprations are core baking and-vitreous enameling. Onthe other hand, in the treatment of certain metals to prevent scale formation a finely reducatmosphere may produce the bestresults. In the annealing of brass it has been found desirable under certain circumstances to introduce methanol vapor into the furnace. In furnaceswhere combustion efllciency is the prime factor it is, of course, desirable to maintain a fuel-air ratio hich will produce a furnace atmosphere having predetermi ned oxygen content. To increase the oxygencontent above this predetermined amount results in a decrease in combustion-efficiency, and likewise to decrease the oxygen content results a decrease in emciency, due for example to incomplete combustion.

\Oneobject of my invention is to provide a from a qualitative but from a quantitative tandpoint aswell.

A further object of my inventionis to provide method and apparatus for regulating the rate of admissionof an oxidizing or reducing agent to maintain the atmosphere within a furnace at a redetermined or desired condition.

method and apparatus for detecting or determin-' ing the condition of the furnace atmosphere'not umreo STATES. PATENT AND CONTROL METHOD AND APPARATUS James R. Campbell, Glendora, CaliL, minor to General Electric Company, a corporation of i -"2,3z4,s21

OFFICE Application February a, 1939, Serial No. 255,301

apparatus for determining the ratio between the rate of air flow and fuel flow to a furnace. 1

A further object of my invention. is to provide a method'and apparatus for regulating the fuel-air ratio to maintain the atmosphere within a furnace at a predetermined condition.

A still further object is toprovide a method and apparatus for determining the oxygen content in the gases resulting from combustion, and to regulate the fuel-air ratio to. maintain such oxygen content at adesired optimum value.

fFurther objects will be apparent from the description to follow and the drawing, in which:

'The furnacev I maybe taken as representative of any industrial furnace used, for example, in the heat treatment, of metals or for ,use with a vapor generator. It will be evident as the description proceeds that my invention is not concerned with the particular use to which the furnace may be put, but as a matter of fact it may be used to determine quantitatively the condition or composition of anyatmosphere.

I have found that when a fuel is burned the conductivity of the flame produced by such burning is a measure of the fuel-oxygen ratio or fuel-air ratio asit is usually called. .If the fuel is burned in a furnace, it is apparent, that as the composition of the furnace atmosphere is a function of the fuel-air ratio it is therefore also a function. of the conductivity of the flame. Therefore, by determining the conductivity of a flame I'provide a means for readily determining the fuel-air ratio and/or the condition or coniposition of the furnace atmosphere. Assuming,

as an example, that the fuel-air ratio is such as to give perfect combustion, as the ratio is increased or decreased, thereby causing a deficiency or excess of air (reducing and oxidizing atmosphere respectively), the electrical conductivity of the flame will vary in functional relation to such-increase or decrease. In accordance with my invention, I provide means for determining the electrical conductivity of the flame, and thus obtain a measure of the. fuel-air ratio. I may further provide means for controlling one or both of the elements of combustion to maintain a predetermined desired fuel-air ratio.

" Still another object is to provide a method and 5s witmmthe fumaee I how two spaced electrodes 3 and 4 separate from the'bumer 2 and connected in circuit with the secondary 5 of a transformer 6 and a resistance I. The primary 8 of the transformer 6 is connected in circuit with a suitable source of potential indicated at 9 and a current measuring device such as an ammeter III. .II'he electrodes 3 and l are'preferably located so that when the furnace is in operation, that is flame is issuing from the unconfined burner 2, the space between the electrodes is filled with flame. As the conductivity of the flame between the electrodes 3 and 4 changes, due to a change in fuel-air ratio, the impedance of the secondary of the transformer 5 will like wise change, thereby causing a greater or lesser current flow through the primary winding 8 as I well as the secondary winding. Hence the curity and hence to the fuel-air ratio, or compositionor the'furnace atmosphere, the scale I03 and chart Inc may be graduated in units descriptive of such factors, such as for example, "percent total air, fuel-air ratio, percent oxidizing" or percent reducing." The index IOA, scale IIIB and. chart I00 are merely specific forms of exhibiting' means which may take a wide variety of other forms as will be evident to those skilled in the art. 7

. If desired I may also utilize the potential drop across the resistance 1 as a measure of the conare connected through a suitable source of po- Fig. l the fuel-air ratio may be automatically controlled to maintain a predetermined flame conductivity resulting in the maintenance of a desired composition of the furnace atmosphere. This control -may be effected by having the devices II or II regulate the rate of flow of either the fuel or air. As it is usually preferable to regulate the rate of fuel flow in accordance with the heat requirements, I show in FIg. 1 the device II, arranged to position the air regulating valve IO tomaintain a desired ratio between fuel flow and air flow. As shown, arranged to position the valve II is a motor having opposed windings 2I and 22. windings 2| and 22 tential indicated at 23 to the deflecting member of the device II. It will be evident from an inspection of the drawing that upon movement of the deflecting member II in one direction the winding." will be energized, whereas movement in the opposite directionwill effect energization of the winding 2i. By suitable adjustment, as will be readily understood by those familiar with .the art, the deflecting member of device II may ductivity of the flam between the electrodes 3 X ands. Thus in Fig. l I show 9. volt meter II electrically connected across the resistance 1 so that its deflections will correspond to the potential drop thereacross and accordingly to the flame conductivity between the electrodes 3 and 4. The volt meter l I is shown as provided with a cooperating scale IIB which, as explained with reference to the scale IOB, may be graduated in units indicative of the fuel-air ratio, or composition of the furnace atmosphere.

As hereinbefore explained, it i usually desired to maintain a predetermined fuel-air ratio so that the atmosphere within the furnace will have a predetermined composition. The particular composition which will produce optimum results depends upon the use to which the furnace is put. It-is therefore usually desirable to regulate one or more of the agents producing the furnace atmosphere to maintain the composition thereof at a predetermined value which will yield optimum results. Such regulation may be eifected either manually or automatically. Thus in Fig. 1 I show the burner 2 provided with fuel through a conduit l2 and air through a conduit I3. In the conduit I2 is a regulating valve ll provided with a hand wheel I5, and in the conduit I3 is a similar regulating valve I6 provided with a hand wheel II. An operator byobserving the indications of thedevices l0 and/or I I 'may by proper actuation of the hand wheels I! and I! regulate the fuel-air ratio to maintain a predetermined desired composition of the atmosphere within the furnace I.

In the embodiment of my lnvention shown in be caused to assume the position shown when the conductivity of the flame indicates that the fuelair ratio is at the desired value. Upon a change in the fuel-air ratio, the deflecting member I I' by virtue of the consequent change inflame conductivity will move to energize one.or the other of the windings II or 22 to position the valve II in proper direction to restore the desired fuel-air ratio. Upon the fuel-air ratio returning to the desired value the deflecting member of the device II will again assume the position shown.

- The fuel admitted to the furnace I may be controlled to maintain the atmosphere therein at a desired temperature and in Fig. 1 I have diagrammatically illustrated such a control. Suite ably located in the furnace I is a thermocouple '24 connected to a responsive device, such as a millivolt meter 25, having'a deflecting member 26. The deflecting member 26 is shown in the position assumed when the temperature within th furnace I is at the desired value. Upon a change in temperature the member 26 will deflect in one direction or the other, thereby caus ing energization of either winding 21 or 2. of a motor 29 arranged to position .the valve I4. Such positioning of the valve will result in a corresponding change in rate of fuel flow to the fur nace I, thereby causing a change in temperature in desired sense to restore it to the desired value. j

evident that any variation in the fuel-oxy en ratio will be due to a change in the oxygen content of the gas.

In Fig. 2 I have shown such a modification of my invention arranged to determine the oxygen content of the gases resulting from combustion of fuel and air in the furnace I. The apparatus I have shown may also be arranged to control the flow of air and/or fuel to the furnace I to maintain a predetermined-oxygen content of the flue gases.

Referring to Fig. 2, I therein show a sampling tube 40 through which a continuous sample of the flue gases, that is the gases resulting from combustion in the furnace I. is drawn at a constant rate by means of a suitable metering pump 50. The tube 40 has an enlarged section 4t forming a combustion tube wherein the gas may be used to support the combustion of a suitable fuel, such as methanol vapor or methyl alcohol vapor admitted to the combustion tube at a, constant rate through a. metering pump 5|. The

' conductivity of the flame will be a measure of the fuel-oxygen ratio, and as the rate of fuel supply is maintained constant the conductivity of the flame will accordingly become a measure of the oxygen content of the flue gas. As shown,

the electrodes 3 and 4 may be disposed in the flame, and apparatus, such as a current, measuring device 46, connected in the primary of the transformer 6 used to give a visual indication of the oxygen content of the flue gas.

As the oxygen content of the flue gas may vary between-wide limits, to facilitate the ignition of the fuel I may provide a suitable heating element,

"such as indicated at 42, comprising a resistance energized from a source of current indicated at As described with reference to Fig. 1, the modiflcation of my invention shown in Fig. 2 may also be provided with suitable means for automatically regulating the fuel-air ratio to the burner 2. Therein I show the measuring'device 46 arranged to vary the rate of air supply in accordance with changes in the oxygen content in the flue gas. Likewise the rate of, fuel supply to the furnace I may be controlled from temperature to maintain a predetermined desired temperature within the furnace I.

The foregoing description serves merely to illustrate, by specific applications, the principles of my invention and should not be taken as defining the scope thereof. I

What I claim as new,- and desire to secure by Letters Patent of the United States, is:

f 1. The method of determining the ratio between the elements of combustion supplied a furnace flame in variable ratios which includes determining the electrical conductivity of the flame within the furnace resulting from the combustion oftthe elements of'combustion and utilizing such determination as a measure of th ratio between the element of combustion.

2. The method of determining the composition of.- a furnace atmosphere in which fuel and air urned which includes determining the ratio between fuel and air suppliedby measuring the the combustion of the fuel and air.

3. The method of determining the oxygen content of a gas which includes burning a fuel with the gas and determining the electrical conductivity of the flame produced by such burning as a measure of the oxygen content in the gas.

, 4. The method of determining the oxygen con tent of a gas which includes burning methanol ductivity of the flame produced by such burning as a measure of the oxygen content in the gas.

5. The method of determining the oxygen content of a gas which includes burning methyl alcohol with the gas and determining the electrical conductivity of the flame produced by such burning as a measure of the oxygen content of the gas.

6. The'method of determining the oxygen content of a gas which includes supplying fuel and the gas to a burner at constant rates, burning the mixture of fuel and gas, and using the electrical conductivity of the flame produced by such burning as a measure of the oxygen content in the gas.

7. The method of determining the composition of a furnace atmosphere produced by the burning of the elements of combustion which includes determining the electrical conductivity of the flame produced by such burning as a measure of the ratio between the elements of combustion.

8. The method of maintaining a desired fuelair ratio to a furnace which includes, varying the fuel-air ratio in correspondence with changes in the electrical conductivity of .the flame produced by the burning of the fuel and air.

9. The method of maintaining a desired oxygen content in the gases of combustion produced by the burning of the'elements of combustion in a furnace which includes, burning a fuel with the gases of combustion, determining the electrical conductivity of the flame produced by such means to determine the ratio between the elements of combustion supplied the burner com- 'prising means including spaced electrodes separate from the burner to determine the electrical conductivity of the flame issuing from the burner and produced by the burning of the elements of combustion.

11. Apparatus comprising a burner, means for supplying fuel and air to the burner, means to determine the ratio between fuel and air supplied the burner comprising a pair of spaced electrodes disposed to be enveloped in the flame issuing from said burner, an electric circuit including said electrodes, and means for determining the electrical conductivity of said circuit as a measure of the ratio between fuel and air supplied the burner.

12. Apparatus comprising an unconfined burner, means for supplying fuel and oxygen to the electrical conductivity of the flame resulting from with the gas and determining the electrical conburner in variable ratios, means to determine I the ratio between the fuel and oxygen supplied the burner comprising an electric circuit including spaced electrodes separate from the burner and a portion of the flame produced by the burning of the fuel and oxygen, and means to deter-- mine the electrical conductivity of said circuit.

13. Apparatus comprising an unconfined burnductivity of the flame produced by the corribustion, means for determining the electrical conductivity of the flame produced by the combustion of the elements of combustion, means for controlling the ratio between the elements of combustion supplied the furnace in correspondence with the electrical conductivity of the flame, and means for modifying said ratio in accordance with the temperature in the furnace.

16. In combination, means for determining the oxygen content of a gas comprising, a burner, means supplying the gas to said burner at a relatively uniform flow rate, means supplying a fuel to said burner at a relatively uniform flow rate, and means for determining the electrical conductivity of the flame produced by the burning of said gas and fuel as a measure of the oxygen content of the gas.

17. The method of determining the completeness of combustion which includes, determining the electrical conductivity of the flame produced by such combustion, and utilizing the determination as a measure of the completeness of combustion.

18. A combustion quality control system for a fuel burner including fuel and air supply means to establish a flame at said burner, a device to control the mixture of fuel and air supplied to said burner, a pair of spaced electrodes insulated from each other and positioned in the path of said burner flame, a source of electrical energy,

a device to operate said control device, a circuit connecting said source of energy and said second mentioned device, and means controlled by the conductance between said electrodes to control the conductivity of such circuit.

JAMES R. CAMPBELL. 

